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Old Mar 01, 2015, 02:02 PM
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Need help designing a flying wing / XFLR5

Hey guys,

I need some help, as despite weeks of googling and reading, the reality is that I dont know what Im doing and Im not going to learn what I need to know in any reasonable amount of time. I have to make a flying wing design very similar to the attached pics, and I need help to get it done.

The unusual shape is a requirement, I need a fairly thick nose (it will house a vertical EDF in a future stage) and I need the rounded trailing edge as I will eventually mount two tilting props there. You guessed it, the ultimate goal is a trictoper/flying wing VTOL hybrid. Im good with the vertical/multirotor part, the problem is, I dont know a lot about aerodynamics and Ive never ever designed a plane.

The reading I did lead me to use special flying wing airfoils; I picked Fauvel 14% for the central body, because I needed the thickness near the nose, and MH60 for the rest. I added some washout and then imported everything in XFLR5 and looked for the button 'auto adjust to make this fly well'. Unfortunately, there is no such button

Despite many many hours of reading, I can produce awesome wallpapers with charts and visualizations, but I cant seem to get the basics right. I have no idea if this will fly or what I should do to make it fly. I only think I managed to partially understand the stability analysis, from which it was evident I needed some vertical stabilizers (which I added).

But I need to figure out if its stable, I need an idea of speeds at which it will fly at or what I should change to make it fly, I need a very good idea where to put the cg. I also have a hunch I need more camber and Im sure the winglet design could use some idea's beyond 'does this look cool'.

So, is there anyone here who knows something about aerodynamics and ideally XFLR5, who wants to help me tweak this design so that when I go build it (just as glider, or with a single pusher prop initially) , I have at least a reasonable chance of it flying ?

You will find the XFLR5 project file here:
https://mega.co.nz/#!8YFCnQAI!OK61fY...6d53nvqetPF2UY

If there is anything else you need or need to know, please ask. Im willing to give a modest compensation for your time.
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Old Mar 03, 2015, 04:49 PM
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I don't like your altitude
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If you don't get a response here,try the Nurflugal and/or modelling science forums.
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Old Mar 04, 2015, 06:06 PM
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I second the Nurflugal (or the flying wing) forum. While there is a chance someone who could give you an answer is hanging out here, it's almost certain that everyone who can will be there.
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Old Mar 11, 2015, 12:58 PM
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Quote:
Originally Posted by ZoomNBoom View Post
The unusual shape is a requirement, I need a fairly thick nose (it will house a vertical EDF in a future stage) and I need the rounded trailing edge as I will eventually mount two tilting props there. You guessed it, the ultimate goal is a trictoper/flying wing VTOL hybrid. Im good with the vertical/multirotor part, the problem is, I dont know a lot about aerodynamics and Ive never ever designed a plane
In VTOL mode you can get any shape to take-off/land vertically.
What will make matters challenging in "airplane" forward flight mode is: The chord of the outboard sections is extremely narrow AND your span is very small. Great for efficiency, but terrible for handling. This will mean high stall speed and high likelihood of one wing dropping before the other at/near stall ("tip stall" in colloquial terminology).
The thickness of the center section or the particular airfoils you chose is almost irrelevant in comparison.
Is there any room/allowance for increasing the chord and span?
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Old Apr 14, 2015, 02:59 AM
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Sorry for late response, lost track of this thread

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Originally Posted by nuteman View Post
In VTOL mode you can get any shape to take-off/land vertically.
True, but a shape with small cross section will catch less wind and thus hover more easily in windy conditions. ANd of course I need a place to put the tilting props and edf.

Quote:
What will make matters challenging in "airplane" forward flight mode is: The chord of the outboard sections is extremely narrow AND your span is very small. Great for efficiency, but terrible for handling. This will mean high stall speed and high likelihood of one wing dropping before the other at/near stall ("tip stall" in colloquial terminology).
Point taken. However, low speed handling is not that important to me, because landing or low speed flying will be done in multirotor mode. I guess it depends how bad it will turn out to be.

Quote:
The thickness of the center section or the particular airfoils you chose is almost irrelevant in comparison.
Is there any room/allowance for increasing the chord and span?
The span, no, since wings wont be removable, ~1m is as big as I want to go.
I might be able to increase the cord by stretching the leading edge forward, but that will also move the cg forward and that is already a bit of a problem for hovering.

Meanwhile, we've built a foam prototype:



Still needs vertical fins, glassing and electronics, but with some luck we may see what it does in a week or two.
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Old Apr 14, 2015, 04:47 AM
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Another home-brew: http://www.rcgroups.com/forums/showthread.php?t=2055174
My opinion: Yours will have such high wing loading that it gives not much benefit to forward flight mode. You'll eat through your battery in no time.

What you're doing is very similar (in function) to the FireFly6 (http://www.birdseyeview.aero/products/firefly6), so maybe you could get ideas from there.
Note the planform of that one. Transitions with your planform could be challenging.
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Old Apr 14, 2015, 05:10 AM
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A narrow wing span makes for less roll stability
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Old Apr 14, 2015, 07:38 AM
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You're building a Delta Ray! Sure, it's not identical but it's close enough for you to use parameters from the delta ray to figure out CG, control surface sizes and other things too.
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Old Apr 14, 2015, 08:31 AM
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You're building a Delta Ray! Sure, it's not identical but it's close enough for you to use parameters from the delta ray to figure out CG, control surface sizes and other things too.
The plane in the image below?
Seems to me that one has a lot more wing area and much lower wing loading than the tilt-rotor tri-copter arrangement that he will have. That one is a "real" delta planform. His has tons of the rear outboard portion of the "delta" missing and its extremely narrow chord on the outboard sections. There will be a very significant difference at even moderate speeds and a huge difference at slow speeds (without help from vertical thrust). The initiation of transition to vertical thrust could easily be delayed and that plane will drop out of the sky - we've seen this.
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Old Apr 14, 2015, 04:17 PM
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Originally Posted by nuteman View Post
Another home-brew: http://www.rcgroups.com/forums/showthread.php?t=2055174
My opinion: Yours will have such high wing loading that it gives not much benefit to forward flight mode. You'll eat through your battery in no time.
We'll see, but flight time isnt that important if the flight is at high speed. Im looking for range more than flight time and it would be surprising if it doesnt beat a multirotor in that area.

Quote:
What you're doing is very similar (in function) to the FireFly6
(http://www.birdseyeview.aero/products/firefly6), so maybe you could get ideas from there.
Note the planform of that one. Transitions with your planform could be challenging.
Yep, but the firefly does so many things wrong IMO. Y6 is not a good configuration to start with, its inherently inefficient. Then it keeps the rear props windmilling in the airstream, which isnt great either, and the way it transitions using 2 flight controllers and some glue logic, is plain wrong.

Im not afraid of the transition, because I will do it different from everyone else. When flying foward, most vtols pitch downward in multirotor mode, like a traditional multirotor, but if you have a wing, that causes negative lift and needs to be adjusted to pitching upward for level flight. Instead I will always maintain a slight pitch up attitude in forward flight, so the wing actually helps by generating lift. That should also make the transition to airplane mode seamless. I cant do that when moving backwards or sideways, but then that its again not a major concern to me.

Of course, thats all easy to say, the proof is in the pudding but Im confident my concept is good. Less confident about the aerodynamics, and Im already redesigning with increased cord.
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Old Apr 14, 2015, 04:22 PM
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Originally Posted by Rockin Robbins View Post
You're building a Delta Ray! Sure, it's not identical but it's close enough for you to use parameters from the delta ray to figure out CG, control surface sizes and other things too.
Its quite different. Try converting the delta ray to a tricopter and you'll quickly see why.

BTW, my goal is not to have any control surfaces; I'll put some on while testing, but I already have two independently tilting props at the rear, so I hope thrust vectoring (and differential thrust) is all I need for level flight.
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Old Apr 14, 2015, 06:35 PM
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You're going to end up much closer to the Delta Ray layout than what you have now. You need some serious wing area for transition. You can't get to high speed without going through low speed. And your plane has to be stable. Narrow wing chord means no transition between flying and stalling.

What you've designed looks doable for full size but not for a model.
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Old Apr 15, 2015, 06:50 AM
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You need some serious wing area for transition. You can't get to high speed without going through low speed.
I will have an EDF in the nose capable of producing enough lift that it will hover with ease as a t-copter. As forward speed increases, the wing/body will be begin generating lift of its own (remember, unlike the firefly and most others, I will not pitch forward, the firefly wings produce negative lift when flying forward as multirotor), so its just a matter of at what speed the wing produces enough lift that I no longer need the front motor.

Anyway, the points of the limited cord and stall characteristics are being taken to heart, and Im already redesigning to have larger wing surface.
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Old Apr 15, 2015, 10:50 AM
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Quote:
Originally Posted by ZoomNBoom View Post
I will have an EDF in the nose capable of producing enough lift that it will hover with ease as a t-copter. As forward speed increases, the wing/body will be begin generating lift of its own (remember, unlike the firefly and most others, I will not pitch forward, the firefly wings produce negative lift when flying forward as multirotor), so its just a matter of at what speed the wing produces enough lift that I no longer need the front motor.

Anyway, the points of the limited cord and stall characteristics are being taken to heart, and Im already redesigning to have larger wing surface.
Generally the volume of air being drawn in from small to medium sized EDF's won't be enough to generate vertical thrust, especially under some load. The idea is perfect for a full scale jet, but not a model aircraft. You would need multiple EDF's to counteract the weight of your aircraft for vertical take-off; which probably won't work. Plus EDF's aren't efficient enough as VTOL's for model aircraft or multirotors, it has been done although the drawback is limited flight for electric powered aircraft, however, you could try nitro ducted fans... albeit they're harder to find now, even so... there is no shortage of power there, just the fuel.

Since I'm already coming up with idea's might as well give you suggestions too... Have you thought about variable-pitch props? Great Planes introduced them a while back with their line of flat foam planes called Flatouts for their popular Rimfire Outrunners, you may have heard of them. It's a pretty ingenious idea and it basically works using the same principals of helicopter tail rotors. In your case you would use the variable-pitch props to transition from VTOL mode to horizontal flight and back with the aid of a swiveling servo to tilt the rotors.
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Old Apr 16, 2015, 01:47 AM
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[COLOR="Black"][B]Generally the volume of air being drawn in from small to medium sized EDF's won't be enough to generate vertical thrust, especially under some load.
I havent decided yet on what EDF to use, but I have enough space to mount a 92mm one (possibly even bigger). You can find those with 4-5 Kg of static thrust which is far more than I need.

Quote:
Plus EDF's aren't efficient enough as VTOL's for model aircraft or multirotors, it has been done although the drawback is limited flight for electric powered aircraft,
Yes, they are less efficient, but the idea is that it will only be used for take off and landing. More over, an EDF in theory ought to be more efficient than a similar sized prop, its just that the majority of rc EDF's arent tuned for efficiency, but for speed/power for a small diameter (relative to props we would use for a similar wattage). Ideally I would find an EDF thats tuned for low RPMs, or I may make one myself.

Quote:
however, you could try nitro ducted fans... albeit they're harder to find now, even so... there is no shortage of power there, just the fuel.
How did you think to control a nitro engine with a flight controller?
I guess its possibly in theory, but doesnt sound like a good plan to me

Quote:
Since I'm already coming up with idea's might as well give you suggestions too... Have you thought about variable-pitch props?
Yes, I have, and it would be very good for my concept. But Im yet to be convinced they can stand any abuse, and with my concept, if I loose just one prop (or motor), its gonna crash.
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